Continuous process for the use of metal carbonyls for the production of nano-scale metal particles formed of non-noble metals

ABSTRACT

A continuous process for producing nano-scale metal particles includes feeding at least one metal carbonyl into a reactor vessel; exposing the metal carbonyl to a source of energy sufficient to decompose the metal carbonyl and produce nano-scale metal particles; and depositing or collecting the nano-scale metal particles.

TECHNICAL FIELD

The present invention relates to a continuous process for the productionof non-noble metal nano-scale particles using metal carbonyls. By“non-noble metal” is meant a metal other than one of the noble metals(generally considered to be gold, silver, platinum, palladium, iridium,rhenium, mercury, ruthenium and osmium). The resulting nano-scaleparticles are useful for catalysis and other purposes. By the practiceof the present invention, nano-scale particles can be produced frommetal carbonyls and collected with greater speed, precision andflexibility than can be accomplished with conventional processing. Thus,the invention provides a practical and cost-effective means forpreparing such nano-scale particles.

BACKGROUND OF THE INVENTION

Catalysts are becoming ubiquitous in modern chemical processing.Catalysts are used in the production of materials such as fuels,lubricants, refrigerants, polymers, drugs, etc., as well as playing arole in water and air pollution mediation processes. Indeed, catalystshave been ascribed as having a role in fully one third of the materialgross national product of the United States, as discussed by Alexis T.Bell in “The Impact of Nanoscience on Heterogeneous Catalysis” (Science,Vol. 299, pg. 1688, 14 Mar. 2003).

Generally speaking, catalysts can be described as small particlesdeposited on high surface area solids. Traditionally, catalyst particlescan range from the sub-micron up to tens of microns. One exampledescribed by Bell is the catalytic converter of automobiles, whichconsist of a honeycomb whose walls are coated with a thin coating ofporous aluminum oxide (alumina). In the production of the internalcomponents of catalytic converters, an aluminum oxide wash coat isimpregnated with nanoparticles of a platinum group metal catalystmaterial. In fact, most industrial catalysts used today include platinumgroup metals especially platinum, rhodium and iridium or alkaline metalslike cesium, at times in combination with other metals such as iron ornickel.

The size of these particles has been recognized as extremely significantin their catalytic function. Indeed it is also noted by Bell that theperformance of a catalyst can be greatly affected by the particle sizeof the catalyst particles, since properties such as surface structureand the electronic properties of the particles can change as the size ofthe catalyst particles changes.

In his study on nanotechnology of catalysis presented at the Frontiersin Nanotechnology Conference on May 13, 2003, Eric M. Stuve of theDepartment of Chemical Engineering of the University of Washington,described how the general belief is that the advantage of the use ofnano-sized particles in catalysis is due to the fact that the availablesurface area of small particles is greater than that of largerparticles, thus providing more metal atoms at the to optimize catalysisusing such nano-sized catalyst materials. However, Stuve points out thatthe advantages of the use of nano-sized catalyst particles may be morethan simply due to the size effect. Rather, the use of nanoparticles canexhibit modified electronic structure and a different shape with actualfacets being present in the nanoparticles, which provide forinteractions which can facilitate catalysis. Indeed, Cynthia Friend, in“Catalysis On Surfaces” (Scientific American, April 1993, p. 74), positscatalyst shape, and, more specifically, the orientation of atoms on thesurface of the catalyst particles, as important in catalysis. Inaddition, differing mass transport resistances may also improve catalystfunction. Thus, the production of nano-sized metal particles for use ascatalysts on a more flexible and commercially efficacious platform isbeing sought. Moreover, other applications for nano-scale particles arebeing sought, whether for the platinum group metals traditionally usedfor catalysis or other metal particles.

Conventionally, however, catalysts are prepared in two ways. One suchprocess involves catalyst materials being deposited on the surface ofcarrier particles such as carbon blacks or other like materials, withthe catalyst-loaded particles then themselves being loaded on thesurface at which catalysis is desired. One example of this is in thefuel cell arena, where carbon black or other like particles loaded withplatinum group metal catalysts are then themselves loaded at themembrane/electrode interface to catalyze the breakdown of molecularhydrogen into monatomic hydrogen, for its separation into its componentprotons and electrons, with the resulting electrons passed through acircuit as the current generated by the fuel cell; on the opposingsurface, molecular oxygen is separated into monatomic oxygen foreventual combination with the proton and electron to form water. Onemajor drawback to the preparation of catalyst materials through loadingon a carrier particle is in the amount of time the loading reactionstake, which can be measured in hours in some cases.

To wit, in U.S. Pat. No. 6,716,525, Yadav and Pfaffenbach describe thedispersing of nano-scale powders on coarser carrier powders in order toprovide catalyst materials. The carrier particles of Yadav andPfaffenbach include oxides, carbides, nitrides, borides, chalcogenides,metals and alloys. The nanoparticles dispersed on the carriers can beany of many different materials according to Yadav and Pfaffenbach,including precious metals such as platinum group metals, rare earthmetals, the so-called semi-metals, as well as non-metallic materials,and even clusters such as fullerenes, alloys and nanotubes.

Alternatively, the second common methods for preparing catalystmaterials involves directly loading catalyst metals such as platinumgroup metals on a support without the use of carrier particles which caninterfere with the catalytic reaction. For example, many automotivecatalytic converters, as discussed above, have catalyst particlesdirectly loaded on the aluminum oxide honeycomb which forms theconverter structure. The processes needed for direct deposition ofcatalytic metals on support structures, however, are generally operatedat extremes of temperature and/or pressures. For instance, one suchprocess is chemical sputtering at temperatures in excess of 1,500° C.and under conditions of high vacuum. Thus, these processes are difficultand expensive to operate and also involve line-of-sight reactions,precluding fully utilization of the support structure.

In an attempt to provide nano-scale catalyst particles, Bert andBianchini, in International Patent Application Publication No. WO2004/036674, suggest a process using a templating resin to producenano-scale particles for fuel cell applications. Even if technicallyfeasible, however, the Bert and Bianchini methods require hightemperatures (on the order of 300° C. to 800° C.), and require severalhours. Accordingly, these processes are of limited value.

Taking a different approach, Sumit Bhaduri, in “Catalysis With PlatinumCarbonyl Clusters,” Current Science, Vol. 78, No. 11, 10 June 2000,asserts that platinum carbonyl clusters, by which is meant polynuclearmetal carbonyl complexes with three or more metal atoms, have potentialas redox catalysts, although the Bhaduri publication acknowledges thatthe behavior of such carbonyl clusters as redox catalysts is notunderstood in a comprehensive manner. Indeed, metal carbonyls have beenrecognized for use in catalysis in other applications.

Metal carbonyls have also been used as, for instance, anti-knockcompounds in unleaded gasolines. However, more significant uses of metalcarbonyls are in the production and/or deposition of the metals presentin the carbonyl, since metal carbonyls are generally viewed as easilydecomposed and volatile resulting in deposition of the metal and carbonmonoxide.

Generally speaking, carbonyls are transition metals combined with carbonmonoxide and have the general formula M_(x)(CO)_(y), where M is a metalin the zero oxidation state and where x and y are both integers. Whilemany consider metal carbonyls to be coordination compounds, the natureof the metal to carbon bond leads some to classify them asorganometallic compounds. In any event, the metal carbonyls have beenused to prepare high purity metals, although not for the production ofnano-scale metal particles. As noted, metal carbonyls have also beenfound useful for their catalytic properties such as for the synthesis oforganic chemicals in gasoline antiknock formulations.

While, as noted, catalyst materials are traditionally formed of noblemetals, such as the platinum group metals, the formation of nano-scaleparticles, with the resulting surface area and surface effectadvantages, may permit the use of non-noble metals, such as nickel,iron, etc., as catalyst materials. The resulting cost savings can besignificant, and can permit the more widespread use of catalyticreactions in industrial processing.

Accordingly, what is needed is a continuous process for the productionof non-noble metal nano-scale particles for use as, e.g., catalystmaterials. The desired process can be used for the preparation ofnano-scale particles loaded on a carrier particle but, significantly,can also be used for the deposit of catalytic non-noble metal nano-scaleparticles directly on a surface without the requirement for extremes intemperature and/or pressures.

SUMMARY OF THE INVENTION

A continuous process for the production of non-noble metal nano-scaleparticles using metal carbonyl starting materials is presented. Bynano-scale particles is meant particles having an average diameter of nogreater than about 1,000 nanometers (nm), e.g., no greater than aboutone micron. More preferably, the particles produced by the inventivesystem have an average diameter no greater than about 250 nm, mostpreferably no greater than about 20 nm.

The particles produced by the invention can be roughly spherical orisotropic, meaning they have an aspect ratio of about 1.4 or less,although particles having a higher aspect ratio can also be prepared andused as catalyst materials. Aspect ratio refers to the ratio of thelargest dimension of the particle to the smallest dimension of theparticle (thus, a perfect sphere has an aspect ratio of 1.0). Thediameter of a particle for the purposes of this invention is taken to bethe average of all of the diameters of the particle, even in those caseswhere the aspect ratio of the particle is greater than 1.4.

In the practice of the present invention, a non-noble metal carbonyl isfed into a reactor vessel which comprises a conduit and sufficientenergy to decompose the carbonyl applied, such that the carbonyldecomposes and nano-scale metal particles are deposited on a support orcollected in a collector. The carbonyl employed in the invention dependson the nano-scale metal particles desired to be produced. In otherwords, if the desired nano-scale particles comprise nickel and iron, themetal carbonyls employed can be nickel carbonyl, Ni(CO)₄, and ironcarbonyl, Fe(CO)₅. In addition, polynuclear metal carbonyls such asdiiron nonacarbonyl, Fe₂(CO)₉, triiron dodecocarbonyl, Fe₃(CO)₁₂,decacarbonyldimanganese, Mn₂(CO)₁₀ can be employed in the production ofnano-scale metal particles in accordance with the present invention.Indeed, the polynuclear metal carbonyls can be particularly useful wherethe nano-scale metal particles desired are alloys or combinations ofmore than one metallic specie.

The metal carbonyls useful in producing nano-scale metal particles inaccordance with the present invention can be prepared by a variety ofmethods, many of which are described in “Kirk-Othmer Encyclopedia ofChemical Technology,” Vol. 5, pp. 131-135 (Wiley Interscience 1992). Forinstance, metallic nickel and iron can readily react with carbonmonoxide to form nickel and iron carbonyls, and it has been reportedthat cobalt, molybdenum and tungsten can also react carbon monoxide,albeit under conditions of higher temperature and pressure. Othermethods for forming metal carbonyls include the synthesis of thecarbonyls from salts and oxides in the presence of a suitable reducingagent (indeed, at times, the carbon monoxide itself can act as thereducing agent), and the synthesis of metal carbonyls in solvent systemssuch as ammonia. In addition, the condensation of lower molecular weightmetal carbonyls can also be used for the preparation of higher molecularweight species, and carbonylation by carbon monoxide exchange can alsobe employed.

The synthesis of polynuclear and heteronuclear metal carbonyls,including those discussed above, is usually effected by metathesis oraddition. Generally, these materials can be synthesized by acondensation process involving either a reaction induced bycoordinatively unsaturated species or a reaction between coordinativelyunsaturated species in different oxidation states. Although highpressures are normally considered necessary for the production ofpolynuclear and heteronuclear carbonyls (indeed, for any metal carbonylsother than those of transition metals), the synthesis of polynuclearcarbonyls, including manganese carbonyls, under atmospheric pressureconditions is also believed feasible.

It must be borne in mind in working with the metal carbonyls, that carein handling must be used at all times, since exposure to metal carbonylscan be a serious health threat. Indeed, nickel carbonyl is considered tobe one of the more poisonous inorganic industrial compounds. While othermetal carbonyls are not as toxic as nickel carbonyl, care still needs tobe exercised in handling them.

The processing of the metal carbonyls to form nano-scale metal particlesutilizes an apparatus comprising a reactor vessel, at least one feederfor feeding or supplying the non-noble metal carbonyl into the reactorvessel, a support or collector which is operatively connected to thereactor vessel for deposit or collection of nano-scale metal particlesproduced on decomposition of the carbonyl, and a source of energycapable of decomposing the carbonyl. The source of energy should act onthe metal carbonyl(s) employed such that the carbonyl(s) decompose toprovide nano-scale metal particles which are deposited on the support orcollected by the collector.

The reactor vessel can be formed of any material which can withstand theconditions under which the decomposition of the carbonyl occurs.Generally, where the reactor vessel is a closed system, that is, whereit is not an open ended vessel permitting reactants to flow into and outof the vessel, the vessel can be under subatmospheric pressure, by whichis meant pressures as low as about 250 millimeters (mm). Indeed, the useof subatmospheric pressures, as low as about 1 mm of pressure, canaccelerate decomposition of the carbonyl and provide smaller nano-scaleparticles. However, one advantage of the inventive process is theability to produce nano-scale particles at generally atmosphericpressure, i.e., about 760 mm. Alternatively, there may be advantage incycling the pressure, such as from sub-atmospheric to generallyatmospheric or above, to encourage nano-deposits within the structure ofthe carrier particles or supports. Of course, even in a so-called“closed system,” there needs to be a valve or like system for relievingpressure build-up caused, for instance, by the generation of carbonmonoxide (CO) from decomposition of the metal carbonyl or otherby-products. Accordingly, the use of the expression “closed system” ismeant to distinguish the system from a flow-through type of system asdiscussed hereinbelow.

When the reactor vessel is a “flow-through” reactor vessel, that is, aconduit through which the reactants flow while reacting, the flow of thereactants can be facilitated by drawing a partial vacuum on the conduit,although no lower than about 250 mm is necessary in order to draw thereactants through the conduit towards the vacuum apparatus, or a flow ofan inert gas such as argon can be pumped through the conduit to thuscarry the reactants along the flow of the inert gas.

Indeed, the flow-through reactor vessel can be a fluidized bed reactor,where the reactants are borne through the reactor on a stream of afluid. This type of reactor vessel may be especially useful where thenano-scale metal particles produced are intended to be loaded on supportmaterials, like carbon blacks or the like, or where the metal particlesare to be loaded on an ion exchange or similar powdered resinousmaterial.

The at least one feeder supplying the carbonyl into the reactor vesselcan be any feeder sufficient for the purpose, such as an injector whichcarries the metal carbonyl along with a jet of a gas such as an inertgas like argon, to thereby carry the carbonyl along the jet of gasthrough the injector nozzle and into the reactor vessel. The gasemployed can be a reactant, like oxygen or ozone, rather than an inertgas. This type of feeder can be used whether the reactor vessel is aclosed system or a flow-through reactor.

Supports useful in the practice of the invention can be any material onwhich the nano-scale metal particles produced from decomposition of themetal carbonyl can be deposited. In a preferred embodiment, the supportis the material on which the catalyst metal is ultimately destined, suchas the aluminum oxide honeycomb of a catalytic converter in order todeposit nano-scale particles on catalytic converter components withoutthe need for extremes of temperature and pressure required by sputteringand like techniques. Alternatively, a collector suitable for collectingthe nano-scale particles for re-use, such as a cyclonic or centrifugalcollector, is employed.

The support or collector can be disposed within the reactor vessel(indeed this is required in a closed system and is practical in aflow-through reactor). However, in a flow-through reactor vessel, theflow of reactants can be directed at a support positioned outside thevessel, at its terminus, especially where the flow through theflow-through reactor vessel is created by a flow of an inert gas.Alternatively, in a flow-through reactor, the flow of nano-scale metalparticles produced by decomposition of the carbonyl can be directed intoa centrifugal or cyclonic collector which collects the nano-scaleparticles in a suitable container for future use.

The energy employed to decompose the carbonyl can be any form of energycapable of accomplishing this function; indeed, the type or intensity ofenergy employed can depend on the type of carbonyl being decomposed. Forinstance, electromagnetic energy such as infrared, visible, orultraviolet light of the appropriate wavelengths can be employed.Additionally, microwave and/or radio wave energy, or other forms ofsonic energy can also be employed (example, a spark to initiate“explosive” decomposition assuming suitable moiety and pressure),provided the metal carbonyl is decomposed by the energy employed. Thus,microwave energy, at a frequency of about 2.4 gigahertz (GHz) orinduction energy, at a frequency which can range from as low as about180 hertz (Hz) up to as high as about 13 mega Hz, can be employed. Askilled artisan would readily be able to determine the form of energyuseful for decomposing the metal carbonyls which can be employed in theinventive process.

Because of the relatively low decomposition temperature of metalcarbonyls, generally less than about 150° C., and often less than about80° C., one preferred form of energy which can be employed to decomposethe carbonyl is heat energy supplied by, e.g., heat lamps, radiant heatsources, or the like. In such case, the temperatures needed are nogreater than about 250° C. to ensure effective decomposition of a highpercentage of the metal carbonyls in the reactor vessel. Indeed,generally, temperatures no greater than about 200° C. are needed todecompose the carbonyl to effectively produce nano-scale metal particlestherefrom.

Depending on the source of energy employed, the reactor vessel should bedesigned so as to not cause deposit of the nano-scale metal particles onthe vessel itself (as opposed to the support or collector) as a resultof the application of the source of energy. In other words, if thesource of energy employed is heat, and the reactor vessel itself becomesheated to a temperature at or somewhat higher than the decompositiontemperature of the carbonyl during the process of applying heat to thecarbonyl to effect decomposition, then the carbonyl will decompose atthe walls of the reactor vessel, thus coating the reactor vessel wallswith nano-scale metal particles or even bulk metal deposits rather thandepositing or collecting the nano-scale metal particles with the supportor collector (one exception to this general rule occurs if the walls ofthe vessel are so hot that the decomposable carbonyl decomposes withinthe reactor vessel and not on the vessel walls, as discussed in moredetail below).

One way to avoid this is to direct the energy directly at the support orcollector. For instance, if heat is the energy applied for decompositionof the metal carbonyl, the support or collector can be equipped with asource of heat itself, such as a resistance heater in or at a surface ofthe support or collector such that the support or collector is at thetemperature needed for decomposition of the carbonyl and the reactorvessel itself is not. Thus, decomposition occurs at the support orcollector and formation of nano-scale particles occurs principally atthe support or collector. When the source of energy employed is otherthan heat, the source of energy can be chosen such that the energycouples with the support or collector, such as when microwave orinduction energy is employed. In this instance, the reactor vesselshould be formed of a material which is relatively transparent to thesource of energy, especially as compared to the support or collector.

Similarly, especially in situations when the support or collector isdisposed outside the reactor vessel when a flow-through reactor vesselis employed with a support collector at its terminus (whether a solidsubstrate collector for depositing of nano-scale metal particles thereonor a cyclonic or like collector for collecting the nano-scale metalparticles for deposit in a suitable container), the decomposition of thedecomposable carbonyl occurs as the metal carbonyl is flowing throughthe flow-through reactor vessel and the reactor vessel should betransparent to the energy employed to decompose the carbonyl.Alternatively, whether or not the support or collector is inside thereactor vessel, or outside it, the reactor vessel can be maintained at atemperature below the temperature of decomposition of the carbonyl,where heat is the energy employed. One way in which the reactor vesselcan be maintained below the decomposition temperatures of the metalcarbonyl is through the use of a cooling medium like cooling coils or acooling jacket. A cooling medium can maintain the walls of the reactorvessel below the decomposition temperatures of the carbonyl, yet permitheat to pass within the reactor vessel to heat the metal carbonyl andcause decomposition of the carbonyl and production of nano-scale metalparticles in the designed manner.

In an alternative embodiment which is especially applicable where boththe walls of the reactor vessel and the gases in the reactor vessel aregenerally equally susceptible to the heat energy applied (such as whenboth are relatively transparent), heating the walls of the reactorvessel, when the reactor vessel is a flow-through reactor vessel, to atemperature substantially higher than the decomposition temperature ofthe decomposable moiety can permit the reactor vessel walls tothemselves act as the source of heat. In other words, the heat radiatingfrom the reactor walls will heat the inner spaces of the reactor vesselto temperatures at least as high as the decomposition temperature of thedecomposable moiety. Thus, the moiety decomposes before impacting thevessel walls, forming nano-scale particles which are then carried alongwith the gas flow within the reactor vessel, especially where the gasvelocity is enhanced by a vacuum. This method of generatingdecomposition heat within the reactor vessel is also useful where thenano-scale particles formed from decomposition of the decomposablemoiety are being attached to carrier materials (like carbon black) alsobeing carried along with the flow within the reactor vessel. In order toheat the walls of the reactor vessel to a temperature sufficient togenerate decomposition temperatures for the decomposable moiety withinthe reactor vessel, the walls of the reactor vessel are preferablyheated to a temperature which is significantly higher than thetemperature desired for decomposition of the decomposable moiety(ies)being fed into the reactor vessel, which can be the decompositiontemperature of the decomposable moiety having the highest decompositiontemperature of those being fed into the reactor vessel, or a temperatureselected to achieve a desired decomposition rate for the moietiespresent. For instance, if the decomposable moiety having the highestdecomposition temperature of those being fed into the reactor vessel isnickel carbonyl, having a decomposition temperature of about 50° C.,then the walls of the reactor vessel should preferably be heated to atemperature such that the moiety would be heated to its decompositiontemperature several (at least three) millimeters from the walls of thereactor vessel. The specific temperature is selected based on internalpressure, composition and type of moiety, but generally is not greaterthan about 250° C. and is typically less than about 200° C. to ensurethat the internal spaces of the reactor vessel are heated to at least50° C.

In any event, the reactor vessel, as well as the feeders, can be formedof any material which meets the requirements of temperature and pressurediscussed above. Such materials include a metal, graphite, high densityplastics or the like. Most preferably the reactor vessel and relatedcomponents are formed of a transparent material, such as quartz or otherforms of glass, including high temperature glass commercially availableas Pyrex® materials.

Thus, in the process of the present invention, at least one non-noblemetal carbonyl is fed into a reactor vessel where it is exposed to asource of energy sufficient to decompose the carbonyl and producenano-scale metal particles. The metal carbonyl is fed into aclosed-system reactor under vacuum or in the presence of an inert gas;similarly, the carbonyl is fed into a flow-through reactor where theflow is created by drawing a vacuum or flowing an inert gas through theflow-through reactor. The energy applied is sufficient to decompose thecarbonyl in the reactor or as it as flowing through the reactor, andfree the metal from the carbonyl and thus create nano-scale metalparticles which are deposited on a support or collected in a collector.Where heat is the energy used to decompose the carbonyl, temperatures nogreater than about 250° C., more preferably no greater than about 200°C. are required to produce nano-scale metal particles, which at thesurface of the substrate for which they are ultimately intended withoutthe use of carrier particles and in a process requiring only seconds andnot under extreme conditions of temperature and pressure.

In one embodiment of the inventive process, a single feeder feeds asingle carbonyl into the reactor vessel for formation of nano-scalemetal particles. In another embodiment, however, a plurality of feederseach feeds metal carbonyls into the reactor vessel. In this way, allfeeders can feed the same carbonyl or different feeders can feeddifferent carbonyls, such as additional metal carbonyls, so as toprovide nano-scale particles containing different metals such asnickel-iron combinations or nickel-iron combinations as desired, inproportions determined by the amount of the carbonyl fed into thereactor vessel by each feeder. For instance, by feeding differentcarbonyls through different feeders, one can produce a nano-scaleparticle having a core of a first metal, with domains of a second orthird, etc. metal coated thereon. Indeed, altering the carbonyl fed intothe reactor vessel by each feeder can alter the nature and/orconstitution of the nano-scale particles produced. In other words, ifdifferent proportions of metals making up the nano-scale particles, ordifferent orientations of the metals making up the nano-scale particlesis desired, altering the metal carbonyl fed into the reactor vessel byeach feeder can produce such different proportions or differentorientations.

Indeed, in the case of the flow-through reactor vessel, each of thefeeders can be arrayed about the circumference of the conduit formingthe reactor vessel at approximately the same location, or the feederscan be arrayed along the length of the conduit so as to feed metalcarbonyls into the reactor vessel at different locations along the flowpath of the conduit to provide further control of the nano-scaleparticles produced.

While it is anticipated that the inventive process and apparatus mayalso produce particles that are larger than nano-scale in size alongwith the nano-scale particles desired, the larger particles can beseparated from the sought-after nano-scale particles through the use ofthe cyclonic separator or because of their differing deposition rates ona collector.

Therefore it is an object of the present invention to provide a processfor the production of nano-scale metal particles using metal carbonylstarting materials.

It is another object of the present invention to provide a processcapable of producing non-noble metal nano-scale particles underconditions of temperature and/or pressure less extreme than conventionalprocesses.

It is still another object of the present invention to provide a processfor preparing non-noble metal nano-scale particles which can be formedon the end use substrate.

It is yet another object of the present invention to provide a processfor preparing non-noble metal nano-scale particles which can becollected for further use or treatment.

These objects and others which will be apparent to the skilled artisanupon reading the following description, can be achieved by feeding atleast one non-noble metal carbonyl into a reactor vessel comprising aconduit; exposing the non-noble metal carbonyl to a source of energysufficient to decompose the non-noble metal carbonyl and producenano-scale metal particles; and depositing or collecting the nano-scalemetal particles. Preferably, the temperature within the reactor vesselis no greater than about 250° C. The pressure within the reactor vesselis preferably generally atmospheric, but pressures which vary betweenabout 1 mm to about 2000 mm can be employed.

The reactor vessel is advantageously formed of a material which isrelatively transparent to the energy supplied by the source of energy,as compared to either the support or collector or the metal carbonyl,such as where the source of energy is a source of radiant heat. In fact,the support or collector can have incorporated therein a resistanceheater, or the source of energy can be a heat lamp. Where the energy isheat, a cooling medium such as cooling coils or a cooling jacket can bedisposed about the reactor vessel to cool the vessel.

The support can be the end use substrate for the nano-scale metalparticles produced, such as a component of an automotive catalyticconverter or a fuel cell or electrolysis membrane or electrode. Thesupport or collector can be positioned within the reactor vessel.However, the reactor vessel can be a flow-through reactor vesselcomprising a conduit, in which case the support or collector can bedisposed either external to the reactor vessel or within the reactorvessel.

It is to be understood that both the foregoing general description andthe following detailed description present embodiments of the invention,and are intended to provide an overview or framework for understandingthe nature and character of the invention as it is claimed. Theaccompanying drawings are included to provide a further understanding ofthe invention, and are incorporated in and constitute a part of thisspecification. The drawings illustrate various embodiments of theinvention, and together with the description serve to explain theprinciples and operations of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side plan view of an apparatus for the production ofnano-scale metal particles from metal carbonyl starting materialsutilizing a “closed system” reactor vessel in accordance with theprocess of the present invention.

FIG. 2 is a side plan view of an alternate embodiment of the apparatusof FIG. 1.

FIG. 3 is a side plan view of an apparatus for the production ofnano-scale metal particles from metal carbonyl starting materialsutilizing a “flow-through” reactor vessel in accordance with the processof the present invention.

FIG. 4 is an alternative embodiment of the apparatus of FIG. 3.

FIG. 5 is another alternative embodiment of the apparatus of FIG. 3,using a support external to the flow-through reactor vessel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, an apparatus for the production ofnon-noble metal nano-scale particles is generally designated by thenumeral 10 or 100. In FIGS. 1 and 2 apparatus 10 is a closed systemcomprising closed reactor vessel 20 whereas in FIGS. 3-5 apparatus 100is a flow-through reaction apparatus comprising flow-through reactorvessel 120.

It will be noted that FIGS. 1-5 show apparatus 10, 100 in a certainorientation. However, it will be recognized that other orientations areequally applicable for apparatus 10. For instance, when under vacuum,reactor vessel 20 can be in any orientation for effectiveness. Likewise,in flow-through reactor vessel 120, the flow of inert carrier gas andmetal carbonyls or the flow of metal carbonyls as drawn by a vacuum (orcombinations thereof) in FIGS. 3-5 can be in any particular direction ororientation and still be effective. In addition, the terms “up” “down”“right” and “left” as used herein refer to the orientation of apparatus10, 100 shown in FIGS. 1-5.

Referring now to FIGS. 1 and 2, as discussed above apparatus 10comprises a closed-system reactor vessel 20 formed of any materialsuitable for the purpose and capable of withstanding the exigentconditions for the reaction to proceed inside including conditions oftemperature and/or pressure. Reactor vessel 20 includes an access port22 for providing an inert gas such as argon to fill the internal spacesof reactor vessel 20, the inert gas being provided by a conventionalpump or the like (not shown). Similarly, as illustrated in FIG. 2, port22 can be used to provide a vacuum in the internal spaces of reactorvessel 20 by using a vacuum pump or similar device (not shown). In orderfor the reaction to successfully proceed under vacuum in reactor vessel20, it is not necessary that an extreme vacuum condition be created.Rather negative pressures no less than about 1 mm, preferably no lessthan about 250 mm, are all that are required.

Reactor vessel 20 has disposed therein a support 30 which can beattached directly to reactor vessel 20 or can be positioned on legs 32 aand 32 b within reactor vessel 20. Reactor vessel 20 also comprises asealable opening shown at 24, in order to permit reactor vessel 20 to beopened after the reaction is completed to remove support 30 or removenano-scale metal particles deposited on support 30. Closure 24 can be athreaded closure or a pressure closure or other types of closingsystems, provided they are sufficiently air tight to maintain inert gasor the desired level of vacuum within reactor vessel 20.

Apparatus 10 further comprises at least one feeder 40, and preferably aplurality of feeders 40 a and 40 b, for feeding reactants, morespecifically the carbonyl starting materials, into reactor vessel 20. Asillustrated in FIGS. 1 and 2, two feeders 40 a and 40 b are provided,although it is anticipated that other feeders can be employed dependingon the nature of the carbonyl(s) introduced into vessel 20 and/or endproduct nano-scale metal particles desired. Feeders 40 a and 40 b can befed by suitable pumping apparatus for the carbonyl such as venturi pumpsor the like (not shown).

As illustrated in FIG. 1, apparatus 10 further comprises a source ofenergy capable of causing decomposition of the metal carbonyl. In theembodiment illustrated in FIG. 1, the source of energy comprises asource of heat, such as a heat lamp 50, although other radiant heatsources can also be employed. In addition, as discussed above, thesource of energy can be a source of electromagnetic energy, such asinfrared, visible or ultraviolet light, microwave energy, radio waves orother forms of sonic energy, as would be familiar to the skilledartisan, provided the energy employed is capable of causingdecomposition of the carbonyl.

In one preferred embodiment, the source of energy can provide energythat is preferentially couple-able to support 30 so as to facilitatedeposit of nano-scale metal particles produced by decomposition of thecarbonyl on support 30. However, where a source of energy such as heatis employed, which would also heat reactor vessel 20, it may bedesirable to cool reactor vessel 20 using, e.g., cooling tubes 52 (shownpartially broken away) such that reactor vessel 20 is maintained at atemperature below the decomposition temperature of the carbonyl. In thisway, the metal carbonyl does not decompose at the surfaces of reactorvessel 20 but rather on support 30.

In an alternative embodiment illustrated in FIG. 2, support 30 itselfcomprises the source of energy for decomposition of the carbonyl. Forinstance, a resistance heater powered by connection 34 can beincorporated into support 30 such that only support 30 is at thetemperature of decomposition of the metal carbonyl, such that thecarbonyl decomposes on support 30 and thus produces nano-scale metalparticles deposited on support 30. Likewise, other forms of energy fordecomposition of the carbonyl can be incorporated into support 30.

Support 30 can be formed of any material sufficient to have depositthereon of nano-scale metal particles produced by decomposition of thecarbonyl. In a preferred embodiment, support 30 comprises the end usesubstrate on which the nano-scale metal particles are intended to beemployed, such as the aluminum oxide or other components of anautomotive catalytic converter, or the electrode or membrane of a fuelcell or electrolysis cell. Indeed, where the source of energy is itselfembedded in or focused on and associated with support 30, selectivedeposition of the catalytic nano-scale metal particles can be obtainedto increase the efficiency of the catalytic reaction and reduceinefficiencies or wasted catalytic metal placement. In other words, thesource of energy can be embedded within support 30 in the desiredpattern for deposition of catalyst metal, such that deposition of thecatalyst nano-scale metal can be placed where catalytic reaction isdesired.

In another embodiment of the invention, as illustrated in FIGS. 3-5,apparatus 100 comprises a flow-through reactor vessel 120 which includesa port, denoted 122, for either providing an inert gas or drawing avacuum from reactor vessel 120 to thus create flow for the metalcarbonyls to be reacted to produce nano-scale metal particles. Inaddition, apparatus 100 includes feeders 140 a, 140 b, 140 c, which canbe disposed about the circumference of reactor vessel 102, as shown inFIG. 3, or, in the alternative, sequentially along the length of reactorvessel 120, as shown in FIG. 4.

Apparatus 100 also comprises support 130 on which nano-scale metalparticles are collected. Support 130 can be positioned on legs 132 a and132 b or, in the event a source of energy is incorporated into support130, as a resistance heater, the control and wiring for the source ofenergy in support 130 can be provided through line 134.

As illustrated in FIGS. 3 and 4, when support 130 is disposed withinflow-through reactor vessel 120, a port 124 is also provided for removalof support 130 or the nano-scale metal particles deposited thereon. Inaddition, port 124 should be structured such that it permits the inertgas fed through port 122 and flowing through reactor vessel 120 toegress reactor vessel 120 (as shown in FIG. 3). Port 124 can be sealedin the same manner as closure 24 discussed above with respect to closedsystem apparatus 10. In other words, port 124 can be sealed by athreaded closure or pressure closure or other types of closingstructures as would be familiar to the skilled artisan.

As illustrated in FIG. 5, however, support 130 can be disposed externalto reactor vessel 120 in flow-through reactor apparatus 100, and canalso be a structural support 130 as illustrated in FIG. 5. In thisembodiment, flow-through reactor vessel 120 comprises a port 124 throughwhich are impinged on support 130 to thus form and deposit thenano-scale metal particles on support 130. In this way it is no longernecessary to gain access to reactor vessel 120 to collect either support130 or the nano-scale metal particles deposited thereon. In addition,during the impingement on support 130, either port 126 or support 130can be moved in order to provide for the formation of the producednano-scale metal particles on certain specific areas of support 130.This is especially useful if support 130 comprises the end use substratefor the nano-scale metal particles such as the component of a catalyticconverter or electrode for fuel cells. Thus, the nano-scale metalparticles are only deposited where desired and efficiency and decreaseof wasted catalytic metal is facilitated.

As discussed above, reactor vessel 20, 120 can be formed of any suitablematerial for use in the reaction provided it can withstand thetemperature and/or pressure at which decomposition of the carbonylstarting materials occurs. For instance, the reactor vessel should beable to withstand temperatures up to about 250° C. where heat is theenergy used to decompose the carbonyl. Although many materials areanticipated as being suitable, including metals, plastics, ceramics andmaterials such as graphite, preferably reactor vessels 20, 120 areformed of a transparent material to provide for observation of thereaction as it is proceeding. Thus, reactor vessel 20, 120 is preferablyformed of quartz or a glass such as Pyrex® brand material available fromCorning, Inc. of Corning, N.Y.

In the practice of the invention, either a flow of an inert gas such asargon or a vacuum is drawn on reactor vessel 20, 120 and a stream ofmetal carbonyl(s) fed into reactor vessel 20, 120 via feeders 40 a, 40b, 140 a, 140 b, 140 c. For instance, if heat is the source of energy,the carbonyl(s) should be subject to decomposition and production ofnano-scale metal particles at temperatures no greater than 250° C., morepreferably no greater than 200° C. Other materials, such as oxygen, canalso be fed into reactor 20, 120 to partially oxidize the nano-scalemetal particles produced by decomposition of the carbonyl, to modify thenano-scale particles and limit subsequent degradation. Contrariwise, areducing material such as hydrogen can be fed into reactor 20, 120 tofacilitate the decomposition of the metal carbonyl into very pure metalnano-scale particles.

The energy for decomposition of the carbonyl is then provided to thecarbonyl within reactor vessel 20, 120 by, for instance, heat lamp 50,150. If desired, reactor vessel 120 can also be cooled by cooling coils52, 152 to avoid deposit of nano-scale metal particles on the surface ofreactor vessel 20, 120 as opposed to support 30, 130. Nano-scale metalparticles produced by the decomposition of the metal carbonyls are thendeposited on support 30, 130 or, in a cyclonic or centrifugal or othertype collector (not shown), for storage and/or use.

Thus the present invention provides a facile and continuous method forproducing nano-scale metal particles which permits selective placementof the particles, direct deposit of the particles on the end usesubstrate, without the need for extremes of temperature and pressurerequired by prior art processes.

All cited patents, patent applications and publications referred toherein are incorporated by reference.

The invention thus being described, it will be apparent that it can bevaried in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the present invention and allsuch modifications as would be apparent to one skilled in the art areintended to be included within the scope of the following claims.

1. A process for producing non-noble metal nano-scale particles,comprising: a) feeding at least one non-noble metal carbonyl into areactor vessel comprising a conduit; b) exposing the non-noble metalcarbonyl to a source of energy sufficient to decompose the metalcarbonyl and produce nano-scale metal particles; and c) collecting ordepositing the nano-scale metal particles.
 2. The process of claim 1,wherein the temperature within the reactor vessel is no greater thanabout 250° C.
 3. The process of claim 2, wherein a vacuum is maintainedwithin the reactor vessel of no less than about 1 mm.
 4. The process ofclaim 2, wherein a pressure of no greater than about 2 atmospheres ismaintained with the reactor vessel.
 5. The process of claim 1, whereinthe reactor vessel is formed of a material which is relativelytransparent to the energy supplied by the source of energy, as comparedto either a support or a collector on which the nano-scale metalparticles are deposited or collected or the metal carbonyl.
 6. Theprocess of claim 1, where the source of energy comprises a source ofheat.
 7. The process of claim 6, wherein the nano-scale metal particlesare deposited on a support.
 8. The process of claim 7, wherein thesupport has incorporated therein a resistance heater.
 9. The process ofclaim 6, wherein the source of energy comprises a heat lamp.
 10. Theprocess of claim 9, which further comprises cooling the reactor vessel.11. The process of claim 7, wherein the support is the end use substratefor the nano-scale metal particles produced.
 12. The process of claim11, wherein the support comprises a component of an automotive catalyticconverter.
 13. The process of claim 7, wherein the support is positionedwithin the reactor vessel.
 14. The process of claim 1, wherein oxygen isfed into the reactor vessel to partially oxidize the nano-scale metalparticles produced by decomposition of the decomposable moiety.
 15. Theprocess of claim 1, wherein a reducing material is fed into the reactorvessel to reduce the potential for oxidation of the decomposable moiety.